1. Field of the Invention
The present invention relates to life raft inflation equipment. In particular, the present invention relates to an improved raft inflation valve which controls the flow of pressurized gas from a pressure vessel to an inflatable life raft.
2. Description of the Prior Art
Inflatable life rafts have found wide use on ocean-going ships and aircraft. An inflatable life raft offers the advantage of light weight and small size. It is stored in its deflated condition for long periods of time when it is not needed, and yet can be inflated rapidly when it is needed to form a large raft capable of holding relatively large numbers of people.
Inflatable life rafts are inflated using a pressurized inflation gas (such as carbon dioxide, dry air, or nitrogen) which is contained in a pressure tank. When the raft is to be inflated, a valve is actuated by pulling a pull cable which is connected at one end to the valve actuating mechanism in such a manner so as to allow the cable to pull free after the firing mechanism has been actuated. The pull cable is typically connected at its other end to the ship. The pull cable is automatically pulled, therefore, when the raft is thrown overboard or when the ship sinks. The valve opens when actuated to permit the pressurized fluid to expand and fill the life raft.
Originally, and prior to the advent of high pressure technology, all inflation systems used carbon dioxide stored in liquid form in the pressure tank. Carbon dioxide undergoes a phase change from liquid to gas when the valve is actuated and the raft is inflated. Becase of severe thermodynamic effects on temperature caused by the phase change and rapid pressure drop, carbon dioxide has a tendency to freeze (form dry ice) or slush-up in cold weather. This frequently causes a "plugged" valve which results in a slow or partial inflation that can render the raft of little or no emergency use value.
To overcome the shortcomings of the carbon dioxide raft inflation systems, systems using pressurized dry air as the inflation gas were developed and perfected by the U.S. Navy during the middle 70's. The dry air systems do not suffer from the freeze-up problems associated with carbon dioxide systems. They do require, however, that the dry air be stored at a much higher pressure (normally in the range of about 5,000 psi) because dry air does not undergo a phase change expansion like carbon dioxide. The advent of the high pressure dry air systems for life raft inflation required the development of raft inflation valves which were capable of operating reliably at these high pressures, while at the same time offering low activating force. One highly advantageous raft inflation valve has been the Marada Mark VI valve manufactured and sold by Marada Research and Manufacturing of Chaska, Minn. This valve, two of which are used on the U.S. Navy's 25-man Mark VI raft, is a stainless steel valve with a movable spool. The spool is biased by a spring to maintain the valve in a normally closed position. When the pull cable is pulled, it causes a cam to be rotated, which moves the spool against the spring force to open the valve.
The Marada Mark VI valve has provided very reliable operation at the high pressures, and is capable of being actuated with a relatively low pull force on the pull cable (typically less than 20 pounds). The Marada Mark VI valve, however, because of the intricate design and the relatively large number of high precision parts required, has been expensive to manufacture. In addition, like other raft inflation valves, it has been susceptible to contamination if the source of the inflation gas (in this case dry air) contains dust, dirt particles, or other contaminants.
Thus there has been a continuing need for an improved raft inflation valve which provides ultra-high reliability, is capable of handling high pressures (up to for example, 6,000 psi), has a low actuating force, is not affected by contamination or environmental changes, and is easy and relatively inexpensive to manufacture.